Salesforce.com has come under fire from critics who say the "hackathon" it held at last week's Dreamforce conference was judged unfairly, and CEO Marc Benioff is now promising a thorough investigation.

"We are doing a full review of the Hackathon," Benioff said in a Twitter message. "We always respond to feedback, and this will be no different. It must be a legitimate victory."

Contestants in the hackathon competed to make a mobile application using Salesforce.com's technology. The top US$1 million prize went to Upshot, which developed an application that allows users to create and edit Salesforce.com reports from mobile devices.

The official rules for the hackathon allowed coding to begin on an application as of Oct. 25, when the contest was announced. Eligible applications also had to be "developed solely as part of this Hackathon," the rules state.

Posters also complained that Kim is a former Salesforce.com employee, although it doesn't appear his participation was actually in violation of the contest rules. He couldn't be reached for comment Monday.

Other posters identifying themselves as hackathon participants said their entries didn't receive any evaluation from judges.

"We've seen questions about why the winning team was allowed to submit an app that may have used pre-existing code, how the judging worked, and the eligibility of participants," said Adam Seligman, vice president of developer marketing, in a blog post. "While we are conducting a thorough review of the final entries to ensure they complied with published rules and regulations, we wanted to address some of those concerns here."

The language in the rules denoting that applications must be "developed solely" for the Hackathon didn't tell the whole story, Seligman added.

"We expected and encouraged teams to take advantage of existing APIs and services they've written to create a great mobile app," he wrote. "For example, any Salesforce customer or developer is likely to have a whole set of existing customizations and logic that can be exposed to their mobile app via REST API."

Seligman pointed to a thread on Salesforce.com's message board for developers, in which an administrator provided additional information.

"Reusing code you may have written before is fine, provided that you were the author of that code, it doesn't comprise the majority of your app and its use does not violate any third party's rights," states a post dated Nov. 14, prior to the hackathon. "You could modify an existing product to integrate with Salesforce and submit that, however you'd be judged on just that component, not the pre-existing product."

Salesforce.com also put together a team of more than 80 judges, which reviewed every eligible entry "at least twice," Seligman added.

The company will post the results of its review online once it is complete, according to Seligman.